activeadmin_quick_edit_add.rb

# http://helabs.com.br/blog/2014/05/28/quick-add-and-quick-edit-on-active-admin/

# room.rb
  action_item only: :index do
    link_to 'Quick add', admin_room_quick_add_path, class: 'fancybox', data: { 'fancybox-type' => 'ajax' }
  end

  controller do
    def quick_add
      @room = Room.new
      render layout: false
    end

    def quick_create
      @room = Room.new(permitted_params[:room])
      @room.save
      render 'quick_response', layout: false
    end

    def quick_edit
      @room = Room.find(params[:id])
      render layout: false
    end

    def quick_update
      @room = Room.find(params[:id])
      @room.update(permitted_params[:room])
      render 'quick_response', layout: false
    end
  end
  
  # ...
  
  index do
    # ...
    actions defaults: true do |room|
      link_to 'Quick Edit', admin_room_quick_edit_path(room), class: 'fancybox', data: { 'fancybox-type' => 'ajax' }
    end
  end
  
# views/admin/rooms/quick_add.html.haml
  #modal
  %h2 New Room
  %p.modal-description Room Quick Add.

  .section#quick-errors
    -# # = render 'error_messages', object: @room

  .section.form-fluid
    = simple_form_for(@room, url: admin_room_quick_create_path, remote: true) do |f|
      .form-inputs
        = f.input :apartment
        = f.input :rm_num
        = f.input :area
        = f.input :status, as: :select, collection: Room.statuses.keys, include_blank: false
        = f.input :bed_size
        = f.input :window
        = f.input :price
        = f.input :properties
      %ul.form-actions
        %li
          = f.submit 'Save'

# views/admin/rooms/quick_edit.html.haml
#modal
  %h2 Quick Edit Room
  %p.modal-description Edit Room Budget.

  .section#quick-errors
    -# # = render 'error_messages', object: @room

  .section.form-fluid
    = simple_form_for(@room, url: admin_room_quick_update_path, remote: true) do |f|
      .form-inputs
        = f.input :apartment
        = f.input :rm_num
        = f.input :area
        = f.input :status, as: :select, collection: Room.statuses.keys, include_blank: false
        = f.input :bed_size
        = f.input :window
        = f.input :price
        = f.input :properties
      %ul.form-actions
        %li
          = f.submit 'Save'

# views/admin/rooms/quick_response.js.erb
<% if @room.errors.any? %>
  var html = "<%= escape_javascript(render 'error_messages', object: @room) %>";
  $('#quick-add-errors').html(html);
<% else %>
  window.location.reload();
<% end %>

# active_admin.js.coffee
#= require fancybox
$ ->
  $('a.fancybox').fancybox()

# app/assets/stylesheets/active_admin.css.scss:
@import "active_admin/mixins";
@import "active_admin/base";
@import "fancybox";

# routes.rb
    get   '/admin/rooms/new/quick_add' => 'admin/rooms#quick_add', as: :admin_room_quick_add
    post  '/admin/rooms/quick_create' => 'admin/rooms#quick_create', as: :admin_room_quick_create
    get   '/admin/rooms/:id/edit/quick_edit' => 'admin/rooms#quick_edit', as: :admin_room_quick_edit
    patch '/admin/rooms/:id/quick_update' => 'admin/rooms#quick_update', as: :admin_room_quick_update

# Gemfile
gem 'fancybox2-rails'
gem 'simple_form'